Low cardiac output syndrome has been reported after cardiac surgery in patients who have received chronic amiodarone administration. To test for possible cardiac toxicity of amiodarone, the isolated working heart model was used. Chronic administration of amiodarone resulted in decreased heart rate and contractility in normal rats. Spontaneously hypertensive rats which received the drug had decreased heart rate, aortic output, and coronary flow compared to age/sex matched controls prior to ischemia. The conclusions were that chronic administration of amiodarone to normal rats caused a significant decrease in post-ischemia performance. Hypertrophied rat hearts are similarly sensitive to the drug.